GENERAL DISCUSSION 363 



])olav form S~ — C'H-2 — CH2 — NH3+may l)e still more sharply expressed 

 tlian in cysteine due to the absence around the — NH2 group of the 

 carboxyl group, which weakens the transfer. 



Thus there exists a completely clear sequence of i-eactions of all 

 these compounds depending upon the degree of ionization and the 

 degree of polarization of the sulphydryl group. The protective capacity 

 of the thiols proves to be greater the higher the proportion of the ion 

 state in the sulphydryl group. 



One can point to two exi)erimental methods for establishing the 

 di-polar or zwitterion form of the cysteamine and allied compounds : 

 (1) the high values of the dipole moment and the dielectric increment 

 (de/dc) in solution; (2) the analysis of the curves of the potentiometric 

 titration. 



What has been said does not of course constitute an overall theory 

 but only a partial regularity which embraces, however, quite a large 

 number of thiol compounds. I would like once more to emphasize that 

 this regularity has a general significance, not only for the protective 

 action in regard to radiation, but also for many other oxidizing actions 

 on thiol compounds. 



bacq: I would like to stress that the data quoted by Passynsky are 

 in complete agreement with the work of our laboratory. 



barendsen: I would like to give additional information in regard to 

 the protective proj^erties of cysteamine. 



Foch, the Professor of the Medical-Biological Laboratory at Rijswijk, 

 has shown that cysteamine is a good protective substance for mam- 

 malian cells in tissue culture. 



But I have discovered that under a-radiation the defensive effect 

 of cysteamine is insignificant. In this case, the addition of cysteamine 

 recalls the effect of anoxia. I do not think that both mechanisms — 

 the action of anoxia and the defensive properties of the cysteamine 

 are identical, but in both cases the effect of the injury is removed. In 

 the case of a-radiation, because of the high ionization densit}^ consi- 

 derable damage nevertheless occurs which does not allow the protective 

 effect of the cysteamine to emerge to a sufficient extent. 



BACQ : The action of a-irradiation on the growing rootlets of an onion 

 also varies only weakly in the presence of cysteamine. It has been shown 

 in mice that the effect of the action of neutrons is also only insignifi- 

 cantly lessened under the influence of cysteamine even in comparison 

 with the effect of the action of X-rays. Evidently this is a general 

 phenomenon. 



